Northern Harrier

The Northern Harrier is distinctive from a long distance away: a slim, long-tailed hawk gliding low over a marsh or grassland, holding its wings in a V-shape and sporting a white patch at the base of its tail. Up close it has an owlish face that helps it hear mice and voles beneath the vegetation. Each gray-and-white male may mate with several females, which are larger and brown. These unusual raptors have a broad distribution across North America and Eurasia.

Measurements

Both Sexes

Relative Size

Other Names

Hen Harrier (British), Marsh Hawk

Busard Saint-Martin (French)

Aguilucho pálido, Gavilán rastrero, Gavilán sabanero (Spanish)

Cool Facts

Northern Harriers are the most owl-like of hawks (though they’re not related to owls). They rely on hearing as well as vision to capture prey. The disk-shaped face looks and functions much like an owl’s, with stiff facial feathers helping to direct sound to the ears.

Juvenile males have pale greenish-yellow eyes, while juvenile females have dark chocolate brown eyes. The eye color of both sexes changes gradually to lemon yellow by the time they reach adulthood.

Male Northern Harriers can have as many as five mates at once, though most have only one or two. The male provides most of the food for his mates and their offspring, while the females incubate the eggs and brood the chicks.

Northern Harriers hunt mostly small mammals and small birds, but they are capable of taking bigger prey like rabbits and ducks. They sometimes subdue larger animals by drowning them.

Northern Harrier fossils dating from 11,000 to 40,000 years ago have been unearthed in northern Mexico.

The oldest Northern Harrier on record was 15 years, 4 months old when it was captured and released in 2001 by a bird bander in Quebec.

Habitat

Grassland

Breeding Northern Harriers are most common in large, undisturbed tracts of wetlands and grasslands with low, thick vegetation. They breed in freshwater and brackish marshes, lightly grazed meadows, old fields, tundra, dry upland prairies, drained marshlands, high-desert shrubsteppe, and riverside woodlands across Canada and the northern United States. Western populations tend to breed in dry upland habitats, while northeastern and Midwestern populations tend to breed in wetlands. During winter they use a range of habitats with low vegetation, including deserts, coastal sand dunes, pasturelands, croplands, dry plains, grasslands, old fields, estuaries, open floodplains, and marshes.

Food

Mammals

Northern Harriers forage on the wing, coursing low over the ground. Unlike other hawks, they rely heavily on their sense of hearing to capture prey. In the breeding season they eat small mammals, reptiles, amphibians, and birds. During winter, harriers in the northern part of the range feed almost exclusively on meadow voles; they also eat deer mice, house mice, shrews, rabbits, and songbirds (including meadowlarks, Northern Cardinals, and Song Sparrows). Harriers wintering in the southern part of their range eat cotton rats, house mice, harvest mice, rice rats, shrews, and songbirds.

Nest Description

Males sometimes start building a nest platform and the female finishes it. Later, both sexes bring in nesting material but the female takes charge of arranging them to form the nest. The nest platform is made with thick-stalked plants like cattails, alders, and willows. The inner lining uses grasses, sedges, and rushes. Nest building takes 1–2 weeks. The outside of the nest measures 16–24 inches wide by 1.5–8 inches high, while the interior is 8–10 inches wide by 2–4 inches deep.

Nest Placement

Ground

Either the male or the female chooses the nest site, which is on the ground and usually in a dense clump of vegetation such as willows, grasses, sedges, reeds, bulrushes, and cattails.

Behavior

Soaring

Northern Harriers usually fly slowly and low over the ground, their wings held in a V-shape as they glide. Most males have either one mate or two mates at a time, but some have up to five mates when food is abundant. Each male courts females and advertises his territory by performing sky-dancing displays: undulating, rollercoaster-like flights up to 1,000 feet off the ground, sometimes covering more than half a mile. Although they don’t protect large territories, both males and females vigorously defend the nest itself. Nesting females usually chase away other females, and males chase other males. Females incubate eggs and brood chicks, while males provide most of the food for the females and nestlings. Nest predators include coyotes, feral dogs, striped skunks, raccoons, red foxes, American Crows, Common Ravens, and Great Horned Owls. Livestock and deer sometimes trample eggs and nestlings underfoot. Juvenile harriers play (and hone their hunting skills) by pouncing on inanimate objects like vole-sized corncobs. In winter, Northern Harriers roost in groups on the ground, sometimes with Short-eared Owls. The larger females are dominant to the males.

Conservation

Northern Harriers are fairly common, but their populations are declining. The North American Breeding Bird Survey records a steady decline of 0.8 percent per year from 1966 to 2010, resulting in a cumulative loss of 30 percent, with Canadian populations declining more than U.S. populations. Partners in Flight estimates the global breeding population at 1.4 million, with 35 percent spending some part of the year in the U.S., 17 percent in Canada, and 10 percent in Mexico. They rate an 11 out of 20 on the Continental Concern Score and are not on the 2012 Watch List. Habitat loss has contributed to reduced harrier populations as people have drained wetlands, developed land for large-scale agriculture, and allowed old farmland to become reforested. The small mammals that harriers prey upon have been reduced because of overgrazing, pesticides, and reduced shrub cover from crop field expansion. Because they eat small mammals, Northern Harriers are susceptible to the effects of pesticide buildup as well as direct effects by eating poisoned animals. In the mid-twentieth century their populations declined from contamination by DDT and other organochlorine pesticides, but rebounded after DDT restrictions went into effect in the 1970s. Northern Harriers have been mostly safe from hunting because of their reputation for keeping mouse populations in check, but they are still sometimes shot at communal winter roosts in Texas and the southeastern United States.

Migration

Resident to long-distance migrant. Harriers are leapfrog migrants, with individuals from northern breeding populations wintering farther south than individuals from southern breeding populations. They usually migrate alone and during daytime, hunting as they go.

Find This Bird

In fall through spring, look for harriers in wide-open grasslands, marshes, or fields. You’re most likely to notice Northern Harriers when they are flying. Note the low, slow, coursing flight style, the bird’s V-shaped wing posture, and its white rump. During migration in the fall and spring, you can also see harriers high in the sky over mountain ridges and coastlines.